The production of thiophene from by-product refinery gases by reacting hydrogen sulfide or sulfur with n-butane, n-butylene and butadiene has been studied for many years. One of the early refinery processes as disclosed in U.S. Pat. No. 2,450,658 reacted butane or butylene with sulfur at temperatures within the range of 1100.degree. to 1300.degree.F. in a stainless steel reactor tube to produce thiophene and tar residues. In this non-catalytic process almost as much by-product tar was produced as the desired thiophene.
In U.S. Pat. No. 2,450,659 the inventors in describing the reaction of butane and sulfur in the vapor phase noted that the reaction proceeds with extreme speed, the only limitation apparently being the rapidity with which heat can be supplied to the reaction mixture.
In U.S. Pat. No. 2,558,507 the patentees reacted butylene with hydrogen sulfide over alumina catalyst to produce thiophene. In U.S. Pat. No. 2,570,722 the patentees reacted butylene with a mixture of sulfur dioxide and hydrogen sulfide over dehydrogenation catalysts to produce thiophene.
In U.S. Pat. No. 2,694,074 the patentees reacted butylene with a mixture of hydrogen sulfide and a thermally labile sulfur compound over a dehydrogenation catalyst to produce thiophene. In a similar reaction described in U.S. Pat. No. 2,694,075 butane was reacted with hydrogen sulfide over a dehydrogenation catalyst to produce thiophene. In this reaction catalyst contact time was in the range of 0.2 to 2 seconds and at a mole ratio of 0.5 to 6 moles of hydrogen sulfide per mole of butane. Catalyst life was in the order of about 75 minutes.
The production of thiophene from butane or butene and hydrogen sulfide is also made difficult by the extremely corrosive conditions encountered at reaction temperatures which cause excessive reactor metal loss. This is particularly true where large amounts of heat must be transferred through reactor walls to overcome the heat loss due to endothermic reactions. These problems were observed in U.S. Pat. No. 2,562,238 where butane was reacted with sulfur to produce thiophene and tars.